Ascorbate peroxidases and cytochrome C peroxidases. Ascorbate peroxidases are a subgroup of heme-dependent peroxidases of the plant superfamily that share a heme prosthetic group and catalyze a multistep oxidative reaction involving hydrogen peroxide as the electron acceptor. Along with related catalase-peroxidases, ascorbate peroxidases belong to class I of the plant superfamily. Ascorbate peroxidases are found in the chloroplasts and/or cytosol of algae and plants, where they have been shown to control the concentration of lethal hydrogen peroxide molecules. The yeast cytochrome c peroxidase is a divergent member of the family; it forms a complex with cytochrome c to catalyze the reduction of hydrogen peroxide to water.

Heme-dependent peroxidases similar to plant peroxidases. Along with animal peroxidases, these enzymes belong to a group of peroxidases containing a heme prosthetic group (ferriprotoporphyrin IX), which catalyzes a multistep oxidative reaction involving hydrogen peroxide as the electron acceptor. The plant peroxidase-like superfamily is found in all three kingdoms of life and carries out a variety of biosynthetic and degradative functions. Several sub-families can be identified. Class I includes intracellular peroxidases present in fungi, plants, archaea and bacteria, called catalase-peroxidases, that can exhibit both catalase and broad-spectrum peroxidase activities depending on the steady-state concentration of hydrogen peroxide. Catalase-peroxidases are typically comprised of two homologous domains that probably arose via a single gene duplication event. Class II includes ligninase and other extracellular fungal peroxidases, while class III is comprised of classic extracellular plant peroxidases, like horseradish peroxidase.

Horseradish peroxidase and related secretory plant peroxidases. Secretory peroxidases belong to class III of the plant heme-dependent peroxidase superfamily. All members of the superfamily share a heme prosthetic group and catalyze a multistep oxidative reaction involving hydrogen peroxide as the electron acceptor. Class III peroxidases are found in the extracellular space or in the vacuole in plants where they have been implicated in hydrogen peroxide detoxification, auxin catabolism and lignin biosynthesis, and stress response. Class III peroxidases contain four conserved disulphide bridges and two conserved calcium binding sites.